A process for treating produced water from offshore oil and gas platforms

Abstract

This invention belongs to the field of offshore water treatment technology, specifically a process for treating production water on offshore oil and gas platforms. The invention includes a hydrocyclone, an oil skimmer, a compact flotation unit, and a production water deaeration tank. The inlet of the hydrocyclone is connected to the outlet of the production water inlet pipe. The hydrocyclone is connected to both the oil skimmer and the compact flotation unit, which in turn is connected to both the oil skimmer and the production water deaeration tank. The hydrocyclone contains several spare pipes and a distributor, and employs tangential feeding. This invention offers the advantage of excellent separation performance, solving the problem that when the production water volume is low, the flow velocity in a single hydrocyclone tube decreases, affecting the separation effect.

Description

Technical Field

[0001] This utility model belongs to the field of marine water treatment technology, and in particular relates to a production water treatment process for offshore oil and gas platforms. Background Technology

[0002] Oily wastewater generated by offshore oil and gas platforms mainly consists of formation water carried from the formation by crude oil, also known as production water. Offshore oil and gas platforms have two possible disposal methods for this production water: one is to treat it to meet standards before discharging it into the sea; the other is to treat it to injection water quality and then inject it into the formation. Based on the characteristics of offshore platform production, the "hydrocyclone + compact flotation unit" technology is currently widely used to treat production water. This method has a small footprint, no rotating parts, requires minimal maintenance, and the separation effect is not affected by ship movement. However, it also has the following disadvantages: Hydrocyclone: ​​A hydrocyclone designed for maximum capacity. When the production water volume is small, the flow velocity of a single hydrocyclone tube decreases, affecting the separation effect.

[0003] Compact Flotation Unit (CFU): A compact flotation unit designed for maximum throughput. When the production water volume is small, the inlet flow rate of the CFU decreases, resulting in poor separation effect; the air flotation efficiency is low; the inlet design cannot form a stable vortex, leading to poor oil-water separation effect.

[0004] Shear force: Centrifugal pumps used to transport production water generate high shear force due to their high rotation speed (>2900 r / min), which causes oil droplets to be sheared and broken, exacerbating oil-water emulsification and making separation difficult; after the production water passes through the regulating valve and the reduced-bore ball valve, the shear force will also cause oil-water emulsification. Utility Model Content

[0005] To overcome the shortcomings of the existing technology, this invention provides a production water treatment process for offshore oil and gas platforms. This invention has the advantage of good separation effect, solving the problem that when the production water volume is small, the flow velocity of a single cyclone tube decreases, affecting the separation effect.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A process for treating production water on offshore oil and gas platforms includes a hydrocyclone, a skimming tank, a compact flotation unit, and a production water deaeration tank. The inlet of the hydrocyclone is connected to the outlet of the production water inlet pipe. The hydrocyclone is connected to both the skimming tank and the compact flotation unit. The compact flotation unit is connected to both the skimming tank and the production water deaeration tank. The hydrocyclone is equipped with several spare pipes and a distributor, and tangential feeding is adopted.

[0007] Preferably, the hydrocyclone is connected to the skimming tank via a first pipe, the hydrocyclone is connected to the compact flotation unit via a second pipe, the compact flotation unit is connected to the skimming tank via a third pipe, and the compact flotation unit is connected to the production water degassing tank via a fourth pipe; differential pressure transmitters are installed between the first pipe and the production water inlet pipe and between the second pipe and the production water inlet pipe, and both differential pressure transmitters are connected to a differential pressure ratio controller via electrical signals.

[0008] Preferably, the bottom of the compact flotation unit is connected to the liquid outlet of the ejector, the liquid inlet of the ejector is connected to the circulating pump, the air inlet of the ejector is connected to the top of the compact flotation unit, and the liquid inlet of the circulating pump is connected to the compact flotation unit; the liquid outlet of the production water deaeration tank is connected to the production water outlet pipe via the production water pump; and the liquid outlet of the oil skimming tank is connected to the oil outlet pipe via the oil skimming pump.

[0009] Preferably, the skimming pump, the production water pump, and the circulation pump are all low-shear pumps.

[0010] Preferably, level controllers are installed on the oil outlet pipe, the fourth pipe, and the production water outlet pipe.

[0011] Preferably, the production water outlet pipe is also equipped with a production water filter, an oil concentration analyzer in the water, and a production water cooler.

[0012] Preferably, the air inlet end of the injector is connected to the flotation gas inlet pipe.

[0013] Preferably, regulating valves are installed on the first pipe, the second pipe, the fourth pipe and the oil outlet pipe, and the regulating valves are connected to the signal from the liquid level controller at the interface of the upstream separator.

[0014] Preferably, the compact flotation unit is also equipped with a V-shaped notch skimming weir, an oil pad, and two anti-vortex baffles. The top of the compact flotation unit is connected to the air inlet of the circulating flotation gas pipe, the air outlet of the circulating flotation gas pipe is connected to the air inlet of the ejector, the outlet of the ejector corresponds to the distributor, and the liquid inlet of the circulating pump is used in conjunction with the anti-vortex baffles.

[0015] Preferably, a third pipe and a CFU outlet pipe are connected to one side of the compact flotation unit. The third pipe is used in conjunction with a V-shaped notch skimming weir, and the CFU outlet pipe is used in conjunction with an anti-vortex baffle.

[0016] The advantages of this utility model are: (1) This utility model uses a certain number of spare tubes in the hydrocyclone to ensure the flow rate of each hydrocyclone tube. By changing to tangential feeding, the fluid enters tangentially along the cylinder wall, which accelerates the migration of oil droplets to the wall surface and achieves better separation effect. A distributor is added in the hydrocyclone to evenly distribute the air bubbles, so that the flow rate is evenly distributed.

[0017] (2) This utility model uses a compact flotation device with a dual-inlet design. When the flow rate is low, one inlet is closed to maintain a higher flow rate. Through tangential feeding, a stable vortex is formed inside the compact flotation device to perform centrifugal separation of the three phases of oil, water and gas in the medium. By using ejectors and distributors, the rising speed of oil droplets is increased. The flotation gas is discharged from the top of the compact flotation device and circulated back to the inlet to minimize the consumption of flotation gas. At the same time, the specially designed V-shaped notch skimming weir enhances the enrichment effect of the oil phase at the weir mouth, continuously skimming oil and avoiding re-emulsification of oil and water. The oil pad provided can enhance the flotation separation effect.

[0018] (3) The present invention uses low shear pumps for circulation pump, skimming pump and production water pump, which can reduce oil-water emulsification; by moving the regulating valve backward, the influence of the regulating valve's shearing effect on the hydrocyclone separation performance is eliminated. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention.

[0020] Figure 2 This is a schematic diagram of the compact flotation device structure of this utility model.

[0021] The meanings of the symbols in the diagram are as follows: 1-Hydrocyclone, 2-Skimming tank, 3-Skimming pump, 4-Compact flotation unit, 5-Production water deaeration tank, 6-Production water pump, 7-Production water filter, 8-Production water cooler, 9-Circulation pump, 10-Ejector, 11-Oil concentration analyzer in water, 12-Production water inlet pipe, 13-Oil outlet pipe, 14-Flotation gas inlet pipe, 15-Production water outlet pipe, 16-Regulating valve, 17-Differential pressure transmitter, 18-Differential pressure ratio controller, 19-Level controller, 20-Level controller signal from upstream separator interface, 21-V-notch skimming weir, 22-Oil pad, 23-Distributor, 24-Anti-vortex baffle, 25-Second pipe, 26-Third pipe, 27-Fourth pipe, 28-Circulating flotation gas pipe. Detailed Implementation

[0022] like Figure 1-2 As shown, a production water treatment process for offshore oil and gas platforms includes a hydrocyclone 1, an oil skimmer 2, a compact flotation unit 4, and a production water deaeration tank 5. The inlet of the hydrocyclone 1 is connected to the outlet of the production water inlet pipe 12. The hydrocyclone 1 is connected to both the oil skimmer 2 and the compact flotation unit 4. The compact flotation unit 4 is connected to both the oil skimmer 2 and the production water deaeration tank 5. The hydrocyclone 1 is equipped with several spare pipes and a distributor 23, and tangential feeding is adopted.

[0023] Specifically, hydrocyclone 1 is connected to oil skimming tank 2 via a first pipe, and hydrocyclone 1 is connected to compact flotation unit 4 via a second pipe 25, which is the CFU production water inlet pipe; compact flotation unit 4 is connected to oil skimming tank 2 via a third pipe 26, which is the CFU oil outlet pipe; compact flotation unit 4 is connected to production water degassing tank 5 via a fourth pipe 27, which is the CFU water outlet pipe; differential pressure transmitters 17 are installed between the first pipe and the production water inlet pipe 12 and between the second pipe 25 and the production water inlet pipe 12, and both differential pressure transmitters 17 are connected to differential pressure ratio controllers 18 via electrical signals.

[0024] Furthermore, the bottom of the compact flotation unit 4 is connected to the liquid outlet of the ejector 10, the liquid inlet of the ejector 10 is connected to the circulating pump 9, the air inlet of the ejector 10 is connected to the top of the compact flotation unit 4, and the liquid inlet of the circulating pump 9 is connected to the compact flotation unit 4; the liquid outlet of the production water degassing tank 5 is connected to the production water outlet pipe 15 via the production water pump 6; and the liquid outlet of the oil skimming tank 2 is connected to the oil outlet pipe 13 via the oil skimming pump 3.

[0025] Furthermore, level controllers 19 are installed on the oil outlet pipe 13, the fourth pipe 27, and the production water outlet pipe 15. A production water filter 7, an oil concentration analyzer 11, and a production water cooler 8 are also installed on the production water outlet pipe 15. The air inlet of the ejector 10 is connected to the flotation gas inlet pipe 14. Control valves 16 are installed on the first pipe, the second pipe 25, the fourth pipe 27, and the oil outlet pipe 13, and these control valves 16 are signal-connected to the level controller 19 at the upstream separator interface.

[0026] The compact flotation unit 4 is also equipped with a V-notch skimming weir 21, an oil pad 22, and two anti-vortex baffles 24. The top of the compact flotation unit 4 is connected to the air inlet of the circulating flotation air pipe 28, the air outlet of the circulating flotation air pipe 28 is connected to the air inlet of the ejector 10, the outlet of the ejector 10 corresponds to the distributor 23, the liquid inlet of the circulating pump 9 is used in conjunction with the anti-vortex baffles 24, and the compact flotation unit 4 is also connected to the CFU inlet pipe 25. A third pipe 26 and a CFU outlet pipe 27 are connected to one side of the compact flotation unit 4. The third pipe 26 is used in conjunction with the V-notch skimming weir 21, and the CFU outlet pipe 27 is used in conjunction with the anti-vortex baffles 24. The circulating flotation gas pipe 28 is connected to the flotation gas inlet pipe 14, and the two are subsequently connected to the ejector 10 together; the V-shaped notch skimming weir 21 is located on top of the oil pad 22, the distributor 23 is located on top of the two anti-vortex baffles 24, and the oil pad 22 is located on top of the distributor 23.

[0027] In use, a certain number of spare pipes are configured in the hydrocyclone 1 to ensure the flow rate into each hydrocyclone tube. A return line with a regulating valve 16 is added at the outlet of the hydrocyclone 1 to stabilize the flow rate into the hydrocyclone 1. The key parameters such as the cone angle and inlet / outlet diameter of the hydrocyclone tube are optimized and differentiated. At the same time, the feeding method is changed to tangential feeding, so that the fluid enters tangentially along the cylinder wall, which accelerates the migration of oil droplets to the wall surface and improves separation.

[0028] The compact flotation unit 4 employs a dual-inlet design, closing one inlet to maintain a higher flow rate at low flow rates. Tangential feeding creates a stable vortex within the compact flotation unit 4, enabling centrifugal separation of the oil, water, and gas phases within the medium. The use of proprietary produced water, ejector 10, and distributor 23 increases the oil droplet rising velocity. Flotation gas discharged from the top of the compact flotation unit 4 is recycled back to the inlet, minimizing flotation gas consumption. Simultaneously, a specially designed V-shaped notch skimming weir 21 enhances the enrichment effect of the oil phase at the weir opening, continuously skimming oil and preventing oil-water re-emulsification.

[0029] By using low-shear pumps for circulation pump 9, skimming pump 3, and production water pump 6, the oil-water emulsification phenomenon can be reduced; by moving the regulating valve 16 backward, the influence of the shearing effect of the regulating valve 16 on the separation performance of the hydrocyclone 1 is eliminated.

[0030] The production water treatment process for offshore oil and gas platforms using this invention can achieve an oil content of <25ppm in the produced water, meeting the requirements for discharge or reinjection. This process, through the use of a hydrocyclone 1, solves the problem of reduced flow velocity in a single hydrocyclone tube affecting separation efficiency when the production water volume is low.

[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A production water treatment process for offshore oil and gas platforms, comprising a hydrocyclone (1), a skimming tank (2), a compact flotation unit (4), and a production water degassing tank (5), characterized in that: The inlet of the hydrocyclone (1) is connected to the outlet of the production water inlet pipe (12). The hydrocyclone (1) is connected to the oil skimming tank (2) and the compact flotation unit (4) respectively. The compact flotation unit (4) is connected to the oil skimming tank (2) and the production water degassing tank (5) respectively. The hydrocyclone (1) is equipped with several spare pipes and a distributor (23), and tangential feeding is adopted.

2. The production water treatment process for offshore oil and gas platforms according to claim 1, characterized in that: The hydrocyclone (1) is connected to the skimming tank (2) through the first pipe. The hydrocyclone (1) is connected to the compact flotation unit (4) through the second pipe (25). The compact flotation unit (4) is connected to the skimming tank (2) through the third pipe (26). The compact flotation unit (4) is connected to the production water degassing tank (5) through the fourth pipe (27). Differential pressure transmitters (17) are installed between the first pipe and the production water inlet pipe (12) and between the second pipe (25) and the production water inlet pipe (12). Both differential pressure transmitters (17) are connected to a differential pressure ratio controller (18) via electrical signals.

3. The production water treatment process for offshore oil and gas platforms according to claim 2, characterized in that: The bottom of the compact flotation unit (4) is connected to the liquid outlet of the ejector (10), the liquid inlet of the ejector (10) is connected to the circulating pump (9), the air inlet of the ejector (10) is connected to the top of the compact flotation unit (4), and the liquid inlet of the circulating pump (9) is connected to the compact flotation unit (4). The liquid outlet of the production water degassing tank (5) is connected to the production water outlet pipe (15) via the production water pump (6). The liquid outlet of the oil skimming tank (2) is connected to the oil outlet pipe (13) via the oil skimming pump (3).

4. The production water treatment process for offshore oil and gas platforms according to claim 3, characterized in that: The skimming pump (3), the production water pump (6), and the circulation pump (9) are all low shear pumps.

5. The production water treatment process for offshore oil and gas platforms according to claim 3, characterized in that: Level controllers (19) are installed on the oil outlet pipe (13), the fourth pipe (27) and the production water outlet pipe (15).

6. The production water treatment process for offshore oil and gas platforms according to claim 3, characterized in that: The production water outlet pipe (15) is also equipped with a production water filter (7), an oil concentration analyzer (11) in the water, and a production water cooler (8).

7. The production water treatment process for offshore oil and gas platforms according to claim 3, characterized in that: The air inlet of the injector (10) is connected to the flotation gas inlet pipe (14).

8. The production water treatment process for offshore oil and gas platforms according to claim 3, characterized in that: A regulating valve (16) is installed on the first pipe, the second pipe (25), the fourth pipe (27) and the oil outlet pipe (13). The regulating valve (16) is connected to the liquid level controller (19) at the interface of the upstream separator.

9. The production water treatment process for offshore oil and gas platforms according to claim 3, characterized in that: The compact flotation unit (4) is also equipped with a V-shaped notch skimming weir (21), an oil pad (22), and two anti-vortex baffles (24). The top of the compact flotation unit (4) is connected to the air inlet of the circulating flotation gas pipe (28), the air outlet of the circulating flotation gas pipe (28) is connected to the air inlet of the ejector (10), the outlet of the ejector (10) corresponds to the distributor (23), and the liquid inlet of the circulating pump (9) is used in conjunction with the anti-vortex baffles (24).

10. The production water treatment process for offshore oil and gas platforms according to claim 9, characterized in that: The compact flotation unit (4) is connected to a third pipe (26) on one side. The third pipe (26) is used in conjunction with the V-shaped notch skimming weir (21), and the fourth pipe (27) is used in conjunction with the anti-vortex baffle (24).

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